I changed his gravel and now he's lethargic, discolored, and won't eat

I just changed out my little buddy Louie's gravel for the first time, and a couple days later some bubbles formed on the surface of his water, and the water itself turned a bit cloudy, so I changed it. When I did, the inside of the bowl was a little grimy, almost like there was a soapy film on it, but I didn't use any soap or detergent or anything on the bowl or the new gravel, and I rinsed it thoroughly before putting it in. I honestly don't know what would have caused it. Now Louie's pretty red color has faded, he won't eat (even though before he would gobble everything up), and he is lethargic, either lying at the bottom of the bowl or drifting at the top, facing upwards. His fins are constantly flared as wide as they can go, which is kindof weird for him. He usually has his bottom fin flared, but not his top one. I'm really rather worried about him. If anyone has any advice or help, I would really really appreciate it.